Homeostasis Flashcards
What is dynamic equilbrium
internal environment of the body fluctuating around a specific normal level
what are the 3 things homeostasis is important for
temperatrue
blood glucose
water
how is homeostasis important for temperature
conditions where it will cause enzyme to denature
ensures the maintenance of optimal conditions for enzyme action and cell function
an increase in body temperature above 40 °C would cause enzymes to denature
This is due to an increase in kinetic energy which would result in the breakage of hydrogen bonds holding the enzyme in a specific 3D shape
The active site will change shape and will no longer be complementary to the substrate molecule
An enzyme-substrate complex cannot form and the enzyme cannot catalyse that reaction anymore, leading to less efficient metabolic reactions
how is homeostasis important for blood glucose
Cells also need a constant supply of energy in the form of ATP to work efficiently
Glucose is respired to supply this ATP, meaning that the body needs to carefully monitor and control blood glucose concentrations
how is homeostasis important for water
crucial for the amount of water in the blood to remain constant
Water is lost during excretion of waste products, e.g. urine, and in sweat
The kidneys are responsible for regulating the amount of water in the blood
what is the control mechanism for maintaining body temperature
thermoregulation
how is vasodilation a cooling mechanism
Vasodilation of the blood vessels that supply skin capillaries, supplying the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation
what the cooling mechanisms
Vasodilation of the blood vessels
Sweating
Flattening of hairs
how is sweating a cooling mechanism
Sweat is secreted by sweat glands
This cools the skin by evaporation; heat energy from the body converts liquid water into water vapour
why is sweating less of an effective cooling mechanism during humid conditions
sweat evaporates more slowly due to a reduced concentration gradient between the sweat and the surrounding air
how is flattening of hair a cooling mechanism
The hair erector pili muscles in the skin relax, causing hairs to lie flat
These muscles can be described as effectors, as they respond to a change in body temperature
This stops them from forming an insulating layer of trapped air and allows air to circulate over skin; heat can therefore leave by radiation
what are warming examples
Vasoconstriction of blood vessels that supply skin capillaries
Boosting metabolic rate
Shivering
Erection of hairs
Less sweating
how is vasoconstriction of blood vessels a warming mechanism
During vasoconstriction the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through skin capillaries
Instead, the blood is diverted through shunt vessels, which are deeper in the skin and therefore do not lose heat to the environment
how is boosting metabolic rate a warming mechanism
Most of the metabolic reactions in the body are exothermic and this provides warmth to the body
In cold environments the hormone thyroxine, released from the thyroid gland, increases the basal metabolic rate (BMR), increasing heat production in the body
Adrenaline may also be released to speed up the metabolic rate and release more heat
how is shivering a warming mechanism
This is a reflex action in response to a decrease in core body temperature
This means it is a nervous mechanism, not a hormonal one
In this case muscles are the effectors and they contract in a rapid and regular manner
The metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature
How is the erection of hairs a warming mechanism
The hair erector pili muscles in the skin contract, causing hairs to stand on end
This forms an insulating layer over the skin’s surface by trapping air between the hairs and stops heat from being lost by radiation
how is less sweating a warming mechanism
The sweat glands will secrete less sweat when it is cold
This will reduce the amount of heat lost through the evaporation of sweat
role of the hypothalamus in thermoregulation
Mammals detect external temperatures via thermoreceptors found in the skin and mucous membranes
There are receptors for both heat and cold
These communicate with the hypothalamus along sensory neurones
The hypothalamus will send impulses along motor neurons to effectors to bring about a physiological response to changing external temperatures
does hypothalamus help regulate body temperature
Yes, by monitoring the temperature of the blood flowing through it and initiating homeostatic responses when it gets too high or too low
what is a negative feedback system
reversing a change in the body to bring it back within normal limits
If body temperature rises a negative feedback system will act to lower body temperature, bringing it back to normal
If blood glucose levels drop a negative feedback system will act to raise blood glucose, bringing it back to normal
describe a negative feedback control loop
A receptor detects a stimulus that is involved with a physiological factor
E.g. a change in temperature or blood glucose level
A coordination system transfers information between different parts of the body
- This could be the nervous system or the hormonal system
An effector carries out a response
Effectors are muscles or glands
what is positive feedback
the original stimulus produces a response that causes the factor to deviate even more from the normal range
how can hormones alter events inside a cell
by influencing gene expression
how do eukaryotes control gene expression
using transcription factors
what is a transcription factor
a protein that controls the transcription of genes by binding to a specific region of DNA
what are activators and repressors
transcription factors that increase the rate at which a gene is expressed
transcription factors that decrease the rate at which a gene is expressed
what are hormones that are able to cross cell surface membrane able to do
enter the nucleus and bind to transcription factors that are present there
explain hormonal regulation of body temperature
At normal body temperature a transcription factor known as the thyroid hormone receptor binds to a section of DNA at the start of a gene
This gene codes for a protein that increases the metabolic rate, generating more heat and therefore increasing body temperature
As long as the thyroid hormone receptor is bound to the region of DNA at the start of the gene, the gene will not be expressed; it can be said to be switched off
in cold temperature what will the body release
the hormone thyroxine which binds to the thyroid hormone receptor
Once the hormone and the receptor are bound together the thyroid hormone receptor allows RNA polymerase to bind to the start of the gene; the gene is said to be switched on and its rate of expression will increase
The protein which increases the metabolic rate is produced in larger quantities, leading to an increase in body temperature
what do hormones that cannot cross the cell membrane do
bind to receptors in the cell surface membrane
The binding of these hormones to cell surface membrane receptors activates second messengers
The activated second messenger molecules activate protein kinases enzyme
Active protein kinase enzymes trigger a chain of reactions, known as a cascade, inside the cell
The cascade may result in changes to the activity of transcription factors which may then affect gene expression in the cell
what are the examples of the hormones that bind to receptors in the cell surface membrane
Adrenaline
Insulin
Glucagon
ADH
what is the control of the heartbeat known as
myogenic, which means the heart will beat without any external stimulus
explain the electrical activity in the heart starting from the SAN
The SAN initiates a wave of depolarisation that causes the atria to contract
the depolarisation is prevented from spreading straight to the ventricles due to the non conduction tissue
Instead, the depolarisation is carried to the atrioventricular node (AVN)
This is a region of conducting tissue between atria and ventricles
After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
Purkyne fibres spread around the ventricles and initiate the depolarisation of the ventricles from the apex (bottom) of the heart
This makes the ventricles contract from the bottom upward and blood is forced out of the ventricles into the pulmonary artery and aorta
what is the SAN
a group of cells in the wall of the right atrium
events of the cardiac cycle
Sinoatrial node sends out a wave of excitation
Atria contract
Atrioventricular node sends out a wave of excitation
Purkyne tissue conducts the wave of excitation
Ventricles contract
what can be used to monitor the electrical activity of the heart
Electrocardiography
explain how to carry out electrocardiography
Electrodes that are capable of detecting electric signals are placed on the skin
These electrodes produce an electrocardiogram (ECG)
An ECG shows a number of distinctive electrical waves produced by the activity of the heart
draw the ECG of a healthy heart and label each wave and why it is caused
PQRSTU
The P wave
Caused by the depolarisation of the atria, which results in atrial contraction (systole)
The QRS complex
Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)
This is the largest wave because the ventricles have the largest muscle mass
The T wave
Caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole)
The U wave
Scientists are still uncertain of the cause of the U wave, some think it is caused by the repolarisation of the Purkyne fibres
what does the bigger the wave on the ECG represent
the greater the electrical activity passing through the heart, which results in a stronger contraction
what is tachycardia
When the heart beats too fast it is tachycardic
resting heart rate of over 100 bpm
what is bradycardia
When the heart beats too slow
resting heart rate below 60 bpm
what is ectopic heartbeat
early heartbeat followed by a pause
This could be due to an earlier contraction of either the atria or ventricles
what is fibrillation
An irregular heartbeat will disrupt the rhythm of the heart
The atria or ventricles stop contracting properly
what is cardiac output
volume of blood that is pumped by the heart per unit of time
what is the average cardiac output
4.7 litres of blood per minute when at rest
why does cardiac output increase when an individual is exercising
so that the blood supply can match the increased metabolic demands of the cells
how can CO be calculated
Cardiac output = heart rate x stroke volume
Cardiac output is measured in cm3 min-1
Heart rate is measured in beats per min (bpm)
Stroke volume is measured in cm3
what is stroke volume
volume of blood pumped out of the left ventricle during one cardiac cycle
what is bundle of his
a collection of conducting tissue in the septum (middle) of the heart
describe how thermoregulatory mechanisms are controlled to help marathon runners avoid heat stress
thermoreceptors (in
hypothalamus or skin) detect increase in temperature
{ heat loss / thermoregulatory } centre in hypothalamus stimulated
* (hypothalamus) sends impulses to sweat glands (1)
.
increased blood flow to surface of skin by
{vasodilation / constriction of shunt vessels}
* decreased metabolic rate
parasympathetic and sympathetic
parasympathetic - rest and digest
sympathetic - fight or flight
Explain the role of the nervous system in bringing about the increase in temperature of the fingertip
thermoreceptors detect increase in temperature (1)
- description of role of hypothalamus in heat loss mechanism (1)
- (therefore more) impulses are sent along the sympathetic {nerves / nervous system } (1)
- which leads to constriction of shunt vessels (1)
- therefore causing vasodilation (of arterioles) (1)
- so more warm blood flows near the skin surface (1)
